In conventional electrodeless lamp assemblies, energy is projected into the lamp structure from two field shaping devices, or applicators, which are oriented to face one another so as to define a gap therebetween that accommodates the lamp. The applicators establish a sufficient electromagnetic field in the vicinity of the lamp to initiate and sustain a discharge in the lamp. The applicators are each attached to phased feed points corresponding to respective ends of a planar transmission line.
Current efforts for improving upon the aforementioned lamp assemblies have sought to develop field applicators for optimally and efficiently coupling energy into the lamps. A lamp assembly illustrative of the prior art is disclosed in U.S. Pat. No. 5,070,277, herein incorporated by reference. This assembly uses slow wave applicators made from helical coils which compress the electromagnetic wavelength inside the helix. Further examples of applicator structures for projecting energy into the lamp are found in U.S. Pat. No. 4,041,352 (single-ended excitation), U.S. Pat. No. 4,266,162 (double-ended excitation), and U.S. Pat. No. 5,130,612 (loop applicator).
In each of the above prior art assemblies, the applicators are electrically coupled to one another by planar transmission lines characterized by bends and other discontinuities which affect the propagation of the signal. In particular, the discontinuities are non-identical at the two phased feed points where energy is coupled by the applicators into the lamp structure. Consequently, prior art lamp assemblies exhibit an imbalance in power fed into the applicators, and therefore an imbalance of power deposited into the lamp. Disadvantageously, this power imbalance may affect lamp performance and the temperature distribution inside the lamp.